A joint is the connection between two bones. Joints and their surrounding structures allow you to bend your elbows and knees, wiggle your hips, bend your back, turn your head, and wave your fingers to say bye-bye.Smooth tissue called cartilage and synovium and a lubricant called synovial fluid cushion the joints so bones do not rub together. But increasing age, injury -- even sitting the wrong way or carrying too much weight -- can wear and tear your cartilage. This can lead to a reaction in your joint that can damage your joints and lead to arthritis.The best way to care for your joints is to keep them and your muscles, ligaments, and bones strong and stable.